Avoid trying to normalize unnormalizable types

compiler/rustc_middle/src/ty/sty.rs

@@ -982,7 +982,10 @@ where
     /// different binding level.
     #[track_caller]
     pub fn dummy(value: T) -> Binder<'tcx, T> {
-        assert!(!value.has_escaping_bound_vars());
+        assert!(
+            !value.has_escaping_bound_vars(),
+            "`{value:?}` has escaping bound vars, so it cannot be wrapped in a dummy binder."
+        );
         Binder(value, ty::List::empty())
     }